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Title: Gamete formation via meiotic nuclear restitution generates fertile amphiploid F1 (oat x maize) plants

Author
item KYNAST, RALF - ROYAL BOT. GARDENS AT KEW
item DAVIS, DOUGLAS - UNIVERSITY OF MINNESOTA
item PHILLIPS, RONALD - UNIVERSITY OF MINNESOTA
item Rines, Howard

Submitted to: Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2012
Publication Date: 6/1/2012
Citation: Kynast, R.G., Davis, D.W., Phillips, R.L., Rines, H.W. 2012. Gamete formation via meiotic nuclear restitution generates fertile amphiploid F1 (oat x maize) plants. Sexual Plant Reproduction. 25(2):111-122.

Interpretive Summary: Partial hybrids of the cereals oat and corn have been produced by application of corn pollen to oat florets aided by rescue of developing embryos on culture medium. These oat-corn crosses involve the most unrelated crop species of which we are aware to produce sexual hybrids. The recovered plants, which contain a complete set of oat genes and frequently some portion of the genes of the corn parent, are often partially self-fertile producing seed from which a partial oat-corn hybrid can be perpetuated. The production of a special type of gamete (egg and pollen sperm cells) from plants initially having only a single instead of the usual double sets of genes and yet capable of self-fertility is rare among species. Through cytological analysis of the developmental stages of these special type gametes we were able to describe the mechanism by which these gametes are produced and relate it to models proposed from analysis of unusual gamete development described in some unrelated species. This information is of interest to biologists investigating unusual forms of gamete development involved in species evolution and to crop researchers making wide crosses to transfer economically valued traits such as disease resistance across species.

Technical Abstract: Oat x maize crosses generated hybrid zygotes that by undergoing complete and incomplete uniparental genome loss of the maize genome during embryogenesis resulted in both euhaploid plants that have complete oat chromosome complements and no maize chromosome and aneuhaploid plants that have complete oat chromosome complements and different numbers of individual maize chromosomes. Some haploids were partially fertile by setting seed in up to 50% of self-pollinated spikelets. The high fertility was found to be mainly caused by formation of unreduced gametes (2n = 3x + 0...3 = 21...24) in both male and female gametogenesis via meiotic nuclear restitution. The restitution process as studied in microsporogenesis and pollen formation follows the model of levigatum-type semi-heterotypic divisions, but with a formation of the nuclear membrane at the transition from telophase I to interkinesis according the model of pygaera-type pseudo-homotypic divisions resembling a haploid meiotic restitution. We discuss use and implications of 2n gametes of oat-maize plants in developing novel materials for maize genomics and oat genetic improvement.